Asteroid 138852 (2000 WN10) passed the Earth at a distance of 19 050 000 km (a little under 50 times the distance between the Earth and the Moon), slightly before 9.10 am GMT on Monday 11 November 2013. There was no danger of the asteroid hitting us, though if were to do so it would present a significant threat. 138852 (2000 WN10) is estimated to be between 170 and 540 m in diameter, and an asteroid of this size would be expected to pass directly through the atmosphere, striking the Earth's surface and creating a crater 3-8 km in diameter, as well as causing devastation over a wide area and global climatic effects that would potentially last for decades.
138852 (2000 WN10) was discovered on 20 November 2000 by the Lincoln Near-Earth Asteroid Research project at the Massachusetts Institute of Technology. The designation 2000 WN10 implies that it was the 263rd asteroid discovered in the second half of November 2000 (period 2000 W), while 138852 indicates that it was the 138 852nd asteroid discovered overall (asteroids are not given this longer designation immediately, to ensure that numbered objects are genuine asteroids that have not been previously described).
138852 (2000 WN10) has a 366 day orbital period and an eccentric orbit inclined to the plane of the Solar System that takes it from 0.70 AU from the Sun (i.e. 70% of the average distance at which the Earth orbits the Sun, roughly the distance at which Venus orbits) to 1.30 AU from the Sun (i.e. 130% of the average distance at which the Earth orbits the Sun, inside the orbit of the planet Mars). It is therefore classed as an Apollo Group Asteroid (an asteroid that is on average further from the Sun than the Earth, but which does get closer). However the inclination at which the asteroid orbits means it seldom draws close to any planet other than Earth.
Because the orbital period of 138852 (2000 WN10) is almost exactly one Earth year, close encounters between the planet and the asteroid are a predictable annual event. This has occurred on 11 November since 2012 and will continue to do so till 2015. From 2008-2011 the asteroid passed us on 12 November, and from 2016-2022 it will pass us on 10 November.
See also Asteroid 2013 VN5 passes the Earth - then gets discovered, Asteroid 2013 UJ9 passes the Earth, Asteroid 2013 UV3 passes between the Earth and the Moon, Asteroid 2013 VL detected after it passes the Earth and Asteroid 2013 UK9 passes the Earth.
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